This question is probably rather unsuitable for the Skeptics format as it rather a matter of (professional) opinion. Starting with the last quote you gave, which is from a 2006 WebMD article

no guaranteed safe way to reuse face masks

The way to decrypt that is to read the full quote

"There is currently no simple, reliable way to decontaminate these devices to enable people to use them more than once," said John C. Bailar, co-chairman of the Institute of Medicine (IOM) panel that issued the report.

It depends what one means by "simple [and] reliable". It certainly not as simple and reliable as decontaminating (stainless steel) surgical instruments, for instance, due to materials used in masks.

As for the more specific ideas from the other quotes, in general use of chemicals has not been terribly favored, e.g. a 2009 paper said in its abstract:

The scent of bleach remained noticeable following overnight drying and low levels of chlorine gas were found to off-gas from bleach-decontaminated FFRs when rehydrated with deionized water. UVGI, ethylene oxide (EtO), and VHP were found to be the most promising decontamination methods; however, concerns remain about the throughput capabilities for EtO and VHP. Further research is needed before any specific decontamination methods can be recommended.

And for example regarding EtO

Residual EtO remaining on FFRs following EtO vapor-phase decontamination is not believed to be a concern because the sterilization process includes a final aeration cycle of 4 h to remove residual EtO gas.

So, is EtO "simple and reliable"?! YMMV. Likewise, heat treatment can be more damaging to some masks models than to others, e.g.

This study evaluated five decontamination methods [...] using nine models of NIOSH-certified respirators. [...] Microwave oven irradiation melted samples from two FFR models.

Regarding oven methods more generally it said

The degree to which temperature affects initial filter aerosol penetration and component melting was observed to be model specific (Figs 1 and ​and 2).

Fig. 1. N95 FFR average initial sodium chloride filter aerosol penetration versus temperature. Each data point represents the average initial penetration of three samples (n = 3), unless otherwise noted. ‘A’ indicates five SN95-D FFRs melted, one at 100°C, two at 110°C, and two at 120°C and could not be penetration or airflow resistance tested.

Somewhat similar graph (fig 2.) for P100 respirators skipped here; of three models of P100 tested, none had melted.

Anther 2011 study which focused on two specific respirator models was more optimistic

This study examined the effectiveness of three energetic decontamination methods [ultraviolet germicidal irradiation (UVGI), microwave-generated steam, and moist heat] on two National Institute for Occupational Safety and Health-certified N95 FFRs [...] contaminated with H5N1. [...] when properly implemented, these methods effectively decontaminate H5N1 on the two FFR models tested and do not drastically affect their filtering function; however, other considerations may influence decisions to reuse FFRs.

Yet another 2010 study actually tried to do this decontamination process more than once (3 times to be more precise):

Decontamination and reuse of FFRs is a possible strategy for extending FFR supplies in an emergency; however, the NIOSH respirator certification process does not currently include provisions for decontamination and reuse. Recent studies have investigated the laboratory performance (filter aerosol penetration and filter airflow resistance) and physical integrity of FFRs following one-cycle (1X) processing of various decontamination treatments. The studies found that a single application of some methods did not adversely affect laboratory performance. In the event that healthcare facilities experience dramatic shortages of FFR supplies, multiple decontamination processing may become necessary. This study investigates three-cycle (3X) processing of eight different methods: ultraviolet germicidal irradiation, ethylene oxide, hydrogen peroxide gas plasma, hydrogen peroxide vapor, microwave-oven-generated steam, bleach, liquid hydrogen peroxide, and moist heat incubation (pasteurization). A four-hour 3X submersion of FFR in deionized water was performed for comparison (control). Following 3X treatment by each decontamination and control method, FFRs were evaluated for changes in physical appearance, odor, and laboratory filtration performance. Only the hydrogen peroxide gas plasma treatment resulted in mean penetration levels > 5% for four of the six FFR models; FFRs treated by the seven other methods and the control samples had expected levels of filter aerosol penetration (< 5%) and filter airflow resistance. Physical damage varied by treatment method. Further research is still needed before any specific decontamination methods can be recommended.

As there is probably no reasonable way to meta-analyze these studies, I suspect it comes down to a reviewer's opinion what to infer from them in terms of generalizability.